Within the US, the recipe would be something along these lines:
Since FL 410 is an eastbound altitude
Moderately short, 1-2 hours
- not so short that climbing high isn't worth it, nor so long that the aircraft takes off so heavy with fuel that 410 can only happen as a step-climb
An aircraft that can reach 410
For example, a 737 NG or Max or a ...
Frame challenge: when aircraft are operating below the transition altitude (which in the USA is 18,000' MSL), ATC radar scopes will correct the reported pressure altitude and display the proper MSL figure (rounded to the nearest 100'). If you are only dealing with a small number of flights, you may be able to submit a FOIA request to the FAA and get the ...